[BLANK_AUDIO] Now that we have a basic understanding of the neurocircuit that's involved in our perception of pain. I want to spend a little time talking about how the neural circuitry can be modulated. And the modulations can affect our actual subjective experience of the pain sensation. And then I would like today to describe the different types of pain that. You're going to most commonly encounter during your clinical practice. So, beginning first with how pain can be modulated. There are three general ways that we think of the modulation occurring. The first type of modulation occurs at the level of the communication between the first order and second order sensor neurons. So it occurs in the dorsal horn. Now do you remember the names of the primary fibers, those first order sensory fibers that carry input into the dorsal horn. What types of fibers are they? [BLANK_AUDIO] Take a stab Andre. Type. >> Type A [UNKNOWN]. >> A, but more specifically it was type A-delta. Excellent, and what else? Naomi do you want to take a stab? I was just going to say Type A Delta. >> Okay. And there's one other type of fiber occurring. Stimuli. >> Type C? >> Type C. Okay. So both those fiber types arrive at the dorsal horn of the spinal cord, right? And there are synapses between that first order sensory neuron. Doesn't matter if it's A type A delta, or a type C, the first order sensory neuron synapses in the dorsal horn with a second order sensory neuron, right? Well, interestingly, there's another type of type A fiber. That will be entering the dorsal horn, right along with the type A delta and the type C fibers. And that third type of first order neuron, is called a type A beta neuron fiber. Okay, the a-betas are large, and they're fairly heavily myelinated and they conduct impulses very rapidly. Okay? So, what they do, if you think about it, is they would be arriving at the dorsal horn. At about the same time, or maybe overlapping in the arrival with the type A delta fibers, they'd arrive before input carried by the type C fibers, right? Okay, and then the type A beta fibers synapse with second order sensory neurons. That are carried up the cord by the spinothalamic tract. The second order neuron in the spinothalamic tract arrives where? Stephanie. >> In the brain stem. >> No, spinothalamic means it arrives where, Naomi? >> In the thalamus? >> Exactly. It, the second order neurons will arrive in the thalamus, and then they synapse with a third order neuron. That carries the signal where? Lydia. >> To the primary somatosensory cortex. >> Excellent. So think about this. We've got the a-betas and the a-deltas kind of simultaneously carrying the same signal, right. But the a-beta. Primary century [INAUDIBLE] we're carrying, information related to touch sensation. Okay? Now, how does this work in real life? Have you ever, like, bumped your head? And experience the sharp pain of bumping your head, what do you do next? The answer is not cry. But what, what do we seem to reflexively do? >> Like rub our head. >> Yes, we rub it. So if you think about what's going on, you know, we just bump our head, and it really hurts, we rub it, and we maybe go right? But that rubbing. Is activating type A beta fibers, which carry a touch sensation which gets transmitted along the spinal columnic pathway to the primary somatosensory cortex, and what we are more likely, as we do that rubbing. Were more likely to experience a modulation of the pain. And we tend to perceive more the touch. Does that make sense? And so we, that segmental level of modulation. Can really, decrease our perception of the pain sensation by providing some additional information. Okay. Now the second kind of, modulation is provided through pathways that are just simply referred to as descending inhibitory pathways. And these descending pathways. Can originate, they do originate, in the brain stem. But they could be activated because it, these descending pathways receive signals from other regions of the brain. But when the descending inhibitory pathway is activated, there will be an. Inhibiting signal pass to the dorsal horn. And that signal will inhibit the information that's carried up the spinal climate tract and the reticulate spinal tract. So our perception of the pain will be decreased because of that inhibitory descending pathway. Kind of working, through a very different mechanism, but, you know, the results end up being, well I won't even say that right now. But, we have this third type of modulation. That is provided by what is called the endogenous opioid system. What does endogenous mean? Do we know? >> It's like made in your body. >> Yeah, it originates in the body. So, endogenous opioids, opioids are simply an analgesic, analgesics. Decrease the perception of pain, right? So, the endogenous opioids are very naturally occurring in our body, our enkephalins, endorphins, and something called dynorphins. And those endogenous opioids. Are in very high concentration up in the brain stem they're probably produced there but there are receptors for them in the brains stem and in the spina chord. So, we tend to have this build in analgesic system that can be activated. And help decrease our perception of painful, stimuli. Have you ever seen anybody under the influence of this system? Have, have you become aware of it ever? For me, I became aware of it once when I volunteered at the end of a marathon, at the finish line for a marathon passing out water. You know, people who have just finished running a marathon have experienced very tough physical conditions and. By the next day they will be experiencing pain in various parts of their body. Right, maybe you've known somebody who's run a marathon, but at the finish line they are euphoric. They feel no pain. Right, because there has been, for most often, there's been a pretty massive. Outpouring of those endogenous opioids that are blunting the pain. Within several hours after the marathon is over, that endogenous opioid suppression of the pain will be starting to decrease and they will begin to feel. The aches a little bit more acutely. So, it's thought that together this endogenous opioids system and the descending inhibitory pathways are the two modulating effects that really help to provide the subjective experiences or. They hope to provide the subjective perceptions of the pain experience. And the hope to explain the fact that a stimulus intensity. At any given stimulus intensity. On one day, I might experience that stimulus as painful. On another day, the experience may not seem so painful. And partly it's because of those modulatory pathways. Influencing how I feel about the pain when it occurs.
